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[lldb][RISCV] Implement trap handler unwind plan #166531

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[lldb][RISCV] Implement trap handler unwind plan #166531

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5cf5867
[lldb][RISCV] Implement trap handler unwind plan
sga-sc Oct 23, 2025
f20b5de
[lldb][RISCV] Mark default unwind plans they couldn't be used for tra…
sga-sc Oct 23, 2025
1747631
[lldb] Change GetTrapHandlerUnwindPlan interface
sga-sc Nov 17, 2025
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8 changes: 4 additions & 4 deletions lldb/include/lldb/Target/Platform.h
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Original file line number Diff line number Diff line change
Expand Up @@ -778,8 +778,8 @@ class Platform : public PluginInterface {
/// Try to get a specific unwind plan for a named trap handler.
/// The default is not to have specific unwind plans for trap handlers.
///
/// \param[in] triple
/// Triple of the current target.
/// \param[in] arch
/// Architecture of the current target.
///
/// \param[in] name
/// Name of the trap handler function.
Expand All @@ -788,8 +788,8 @@ class Platform : public PluginInterface {
/// A specific unwind plan for that trap handler, or an empty
/// shared pointer. The latter means there is no specific plan,
/// unwind as normal.
virtual lldb::UnwindPlanSP
GetTrapHandlerUnwindPlan(const llvm::Triple &triple, ConstString name) {
virtual lldb::UnwindPlanSP GetTrapHandlerUnwindPlan(const ArchSpec &arch,
ConstString name) {
return {};
}

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4 changes: 4 additions & 0 deletions lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -735,6 +735,8 @@ UnwindPlanSP ABISysV_riscv::CreateFunctionEntryUnwindPlan() {
plan_sp->AppendRow(std::move(row));
plan_sp->SetSourceName("riscv function-entry unwind plan");
plan_sp->SetSourcedFromCompiler(eLazyBoolNo);
plan_sp->SetUnwindPlanForSignalTrap(eLazyBoolNo);

return plan_sp;
}

Expand All @@ -761,6 +763,8 @@ UnwindPlanSP ABISysV_riscv::CreateDefaultUnwindPlan() {
plan_sp->SetSourceName("riscv default unwind plan");
plan_sp->SetSourcedFromCompiler(eLazyBoolNo);
plan_sp->SetUnwindPlanValidAtAllInstructions(eLazyBoolNo);
plan_sp->SetUnwindPlanForSignalTrap(eLazyBoolNo);

return plan_sp;
}

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5 changes: 2 additions & 3 deletions lldb/source/Plugins/Platform/AIX/PlatformAIX.cpp
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Expand Up @@ -132,9 +132,8 @@ void PlatformAIX::GetStatus(Stream &strm) {

void PlatformAIX::CalculateTrapHandlerSymbolNames() {}

lldb::UnwindPlanSP
PlatformAIX::GetTrapHandlerUnwindPlan(const llvm::Triple &triple,
ConstString name) {
lldb::UnwindPlanSP PlatformAIX::GetTrapHandlerUnwindPlan(const ArchSpec &arch,
ConstString name) {
return {};
}

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2 changes: 1 addition & 1 deletion lldb/source/Plugins/Platform/AIX/PlatformAIX.h
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Expand Up @@ -47,7 +47,7 @@ class PlatformAIX : public PlatformPOSIX {

void CalculateTrapHandlerSymbolNames() override;

lldb::UnwindPlanSP GetTrapHandlerUnwindPlan(const llvm::Triple &triple,
lldb::UnwindPlanSP GetTrapHandlerUnwindPlan(const ArchSpec &arch,
ConstString name) override;

MmapArgList GetMmapArgumentList(const ArchSpec &arch, lldb::addr_t addr,
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87 changes: 83 additions & 4 deletions lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,13 +15,15 @@
#endif

#include "Plugins/Process/Utility/LinuxSignals.h"
#include "Plugins/Process/Utility/lldb-riscv-register-enums.h"
#include "Utility/ARM64_DWARF_Registers.h"
#include "lldb/Core/Debugger.h"
#include "lldb/Core/PluginManager.h"
#include "lldb/Host/HostInfo.h"
#include "lldb/Symbol/UnwindPlan.h"
#include "lldb/Target/Process.h"
#include "lldb/Target/Target.h"
#include "lldb/Utility/ArchSpec.h"
#include "lldb/Utility/FileSpec.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.h"
Expand Down Expand Up @@ -220,6 +222,7 @@ void PlatformLinux::CalculateTrapHandlerSymbolNames() {
m_trap_handlers.push_back(ConstString("_sigtramp"));
m_trap_handlers.push_back(ConstString("__kernel_rt_sigreturn"));
m_trap_handlers.push_back(ConstString("__restore_rt"));
m_trap_handlers.push_back(ConstString("__vdso_rt_sigreturn"));
}

static lldb::UnwindPlanSP GetAArch64TrapHandlerUnwindPlan(ConstString name) {
Expand Down Expand Up @@ -302,12 +305,88 @@ static lldb::UnwindPlanSP GetAArch64TrapHandlerUnwindPlan(ConstString name) {
return unwind_plan_sp;
}

lldb::UnwindPlanSP
PlatformLinux::GetTrapHandlerUnwindPlan(const llvm::Triple &triple,
ConstString name) {
static lldb::UnwindPlanSP GetRISCVTrapHandlerUnwindPlan(ConstString name,
uint32_t fp_flags) {
if (name != "__vdso_rt_sigreturn")
return {};

UnwindPlan::Row row;

// In the signal trampoline frame, sp points to an rt_sigframe[1], which is:
// - 128-byte siginfo struct
// - ucontext struct:
// - 8-byte long (uc_flags)
// - 8-byte pointer (*uc_link)
// - 24-byte struct (uc_stack)
// - 8-byte struct (uc_sigmask)
// - 120-byte of padding to allow sigset_t to be expanded in the future
// - 8 bytes of padding because sigcontext has 16-byte alignment
// - struct sigcontext uc_mcontext
// [1]
// https://github.com/torvalds/linux/blob/master/arch/riscv/kernel/signal.c

constexpr size_t siginfo_size = 128;
constexpr size_t uc_flags_size = 8;
constexpr size_t uc_link_ptr_size = 8;
constexpr size_t uc_stack_size = 24;
constexpr size_t uc_sigmask_size = 8;
constexpr size_t padding_size = 128;

constexpr size_t offset = siginfo_size + uc_flags_size + uc_link_ptr_size +
uc_stack_size + uc_sigmask_size + padding_size;

row.GetCFAValue().SetIsRegisterPlusOffset(gpr_sp_riscv, offset);
for (uint32_t reg_num = gpr_first_riscv; reg_num < gpr_first_riscv + 32;
++reg_num)
row.SetRegisterLocationToAtCFAPlusOffset(reg_num, reg_num * 8, false);
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@lenary lenary Nov 13, 2025

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Do we need a row to say where pc is stored? It's not part of regs 0-31, as far as I can tell.

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@sga-sc sga-sc Nov 14, 2025

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No, pc register is a part of regs 0-31:

llvm-project/lldb/source/Plugins/Process/Utility/lldb-riscv-register-enums.h

Line 19 in 80ae168

gpr_pc_riscv = gpr_first_riscv,

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@lenary lenary Nov 14, 2025

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Ah, interesting.

Should we be pointing to the FP regs in uc_mcontext too?

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@sga-sc sga-sc Nov 17, 2025

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Thank you for your comment, I added FP regs recovery in this plan


size_t fpr_size = 0;
switch (fp_flags) {
case ArchSpec::eRISCV_float_abi_soft:
fpr_size = 0;
break;
case ArchSpec::eRISCV_float_abi_single:
fpr_size = 4;
break;
case ArchSpec::eRISCV_float_abi_double:
fpr_size = 8;
break;
case ArchSpec::eRISCV_float_abi_quad:
fpr_size = 16;
break;
}

if (fpr_size != 0) {
for (uint32_t reg_num = fpr_first_riscv; reg_num < fpr_first_riscv + 32;
++reg_num) {
row.SetRegisterLocationToAtCFAPlusOffset(reg_num, reg_num * fpr_size,
false);
}

// CSR for FP registers always has 32-bit length.
row.SetRegisterLocationToAtCFAPlusOffset(fpr_fcsr_riscv, fpr_fcsr_riscv * 4,
false);
}

UnwindPlanSP unwind_plan_sp = std::make_shared<UnwindPlan>(eRegisterKindLLDB);
unwind_plan_sp->AppendRow(std::move(row));
unwind_plan_sp->SetSourceName("RISC-V Linux sigcontext");
unwind_plan_sp->SetSourcedFromCompiler(eLazyBoolNo);
unwind_plan_sp->SetUnwindPlanValidAtAllInstructions(eLazyBoolNo);
unwind_plan_sp->SetUnwindPlanForSignalTrap(eLazyBoolYes);

return unwind_plan_sp;
}

lldb::UnwindPlanSP PlatformLinux::GetTrapHandlerUnwindPlan(const ArchSpec &arch,
ConstString name) {
llvm::Triple triple = arch.GetTriple();
if (triple.isAArch64())
return GetAArch64TrapHandlerUnwindPlan(name);

if (triple.isRISCV()) {
uint32_t fp_flags = arch.GetFlags() & ArchSpec::eRISCV_float_abi_mask;
return GetRISCVTrapHandlerUnwindPlan(name, fp_flags);
}
return {};
}

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2 changes: 1 addition & 1 deletion lldb/source/Plugins/Platform/Linux/PlatformLinux.h
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,7 @@ class PlatformLinux : public PlatformPOSIX {

void CalculateTrapHandlerSymbolNames() override;

lldb::UnwindPlanSP GetTrapHandlerUnwindPlan(const llvm::Triple &triple,
lldb::UnwindPlanSP GetTrapHandlerUnwindPlan(const ArchSpec &arch,
ConstString name) override;

MmapArgList GetMmapArgumentList(const ArchSpec &arch, lldb::addr_t addr,
Expand Down
4 changes: 2 additions & 2 deletions lldb/source/Target/RegisterContextUnwind.cpp
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Expand Up @@ -907,9 +907,9 @@ RegisterContextUnwind::GetFullUnwindPlanForFrame() {
// substitute plan. Otherwise, use eh_frame.
if (m_sym_ctx_valid) {
lldb::PlatformSP platform = process->GetTarget().GetPlatform();
const ArchSpec arch = process->GetTarget().GetArchitecture();
if (auto unwind_plan_sp = platform->GetTrapHandlerUnwindPlan(
process->GetTarget().GetArchitecture().GetTriple(),
GetSymbolOrFunctionName(m_sym_ctx)))
arch, GetSymbolOrFunctionName(m_sym_ctx)))
return unwind_plan_sp;
}

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